The invention relates to thermistors, or the like electrical components and particularly to a method of defining and/or trimming the contacts of a thermistor, or the like electrical component and even of trimming the thermistor or electrical component itself.
This description will hereafter refer only to a thermistor. However, as will be apparent to persons skilled in the art, other electrical components, such as resistors, capacitors, or the like, are adapted to application of the method of the invention thereto.
The invention is particularly useful in connection with forming and/or trimming thermistor contacts according to the teachings of U.S. application Ser. No. 787,422, filed Apr. 14, 1977, entitled "Method of Adjusting Resistance of a Thermistor". Additionally, the invention may be used to form the thermistor contacts for the thermometer apparatus disclosed in certain embodiments in U.S. application Ser. No. 779,152, filed Mar. 18, 1977, entitled "Fever Thermometer, or the Like Sensor". Both of these applications are incorporated herein by reference for their teachings with respect to the formation and use of thermistors and for all other teachings and disclosures contained therein.
A thermistor is a semiconductor usually of a ceramic like material and comprised of a metallic oxide. Typically, the ceramic thermistor body is formed of a sintered mixture of manganese oxide, nickel oxide, ferric oxide, magnesium chromate or zinc chromate, or the like. A thermistor makes use of the resistive properties of semiconductors. Thermistors have a large negative temperature coefficient of resistivity such that as temperature increases, the resistance of the thermistor decreases.
A thermistor is connected into an electric circuit which utilizes the resistance of the thermistor in some manner. For effecting an electric connection to the thermistor, the thermistor has contacts attached to it.
The ceramic bodies of thermistors are formed in many ways. One typical thermistor is in a wafer form and is multi-sided. The wafer usually is six sided and has two large opposite surfaces and four narrower width peripheral sides defining the large opposite surfaces. A wafer thermistor may, for example, be cut from a larger sheet or other body of thermistor material or it may be molded. The ceramic material of the thermistor may be formed or cut in virtually any size. Various techniques for cutting, grinding or otherwise trimming thermistor bodies to a particular size are well known.
The wafer type of thermistor has electric contacts secured directly to the surface of the semiconductor material of the thermistor. Typically, the thermistor contacts are comprised of metal and may be comprised of silver mixed with glass particles called "frit." The contacts are baked or heat fused on to flat surfaces of the thermistor semiconductor material. Preferably, the attached contact material covers the entirety of any surface of the thermistor to which it is applied, although the material can cover any area less than the entirety of any surface. Depending upon the particular use and application of the thermistor, its contacts are defined on one surface thereof or on different surfaces thereof.
An entire thermistor may be quite small, and a typical thermistor adapted for use in the aforesaid U.S. applications Ser. Nos. 779,152 and 787,422 is a generally six-sided wafer, whose large surfaces are generally squares and whose longest dimension is on the order of 0.060". Forming the contacts on such a small thermistor from contact material by trimming the contact material, or trimming the contact material on the thermistor itself for any other reason, can be very delicate operations requiring very fine movements. It can be quite time consuming and/or require quite expensive instrumentation.
In the thermometer of U.S. application Ser. No. 779,152, the thermistor contacts are each placed in electrical contact with electrical conductors. The thermistor is quite small in size. The conductors are also quite thin and small. Precise emplacement and orientation of the thermistor contacts on the conductors can be quite difficult. If the thermistor has two contacts on one surface of the thermistor, for example, and each contact is to be seated on only one of the two conductors, then if the tiny thermistor is twisted slightly from its correct orientation, one of its contacts may undesirably bridge both of the conductors, thereby short circuiting the thermistor and rendering inoperative any apparatus, such as a thermometer, with which the thermistor is used.
Using expensive instrumentation and/or expending considerable time and effort, an operator can properly define and/or trim the contacts of an even quite small sized thermistor and he can properly emplace such a thermistor on conductors. However, reduction in the amount of time and effort required and elimination of the need for expensive mounting and trimming equipment would be desired.